JP5422068B2 - LED lighting device and vehicle headlamp - Google Patents

Description

  The present invention relates to an LED lighting device for lighting a semiconductor light source composed of a light emitting diode (LED) element, and a vehicle headlamp using the LED lighting device.

An LED (Light Emitting Diode) element as a semiconductor light source is widely used as a vehicular lamp, a traffic light, and an illumination lamp. As a conventional method for adjusting the luminance of such an LED element, there is a method of controlling a current value flowing through the LED element or controlling a current flowing through the LED element by PWM (Pulse Width Modulation).
The LED element can be dimmed by repeating energization and shut-off of the LED element by PWM control. For example, the one that emits white light when the rated current is supplied during full lighting is dimmed. Sometimes, when the current supplied to the LED element is reduced to simply lower the average current, the blue component of the LED element's emission color gradually decreases, and the LED element emits light in a greenish color. In order to prevent such a chromaticity change from occurring in the semiconductor light source, when a current is supplied to the semiconductor light source based on the on / off control signal, a current stipulated in the semiconductor light source at one logic level of the on / off control signal. There is a lighting control circuit that stops the supply of current to the semiconductor light source when the other logic level of the on / off control signal is supplied. (For example, refer to Patent Document 1).

JP 2006-86063 A (paragraph number [0026], FIG. 1)

  The conventional LED lighting device has adjusted the brightness as described above. However, when individually adjusting the brightness of the plurality of LED elements, a power source capable of adjusting the current value or the pulse width is connected to each LED element. Therefore, there is a problem that the lighting circuit is complicated and the cost becomes high.

  The present invention has been made to solve the above-described problems, and an object thereof is to provide an LED lighting device that is small in size, low in cost, and capable of individually adjusting the brightness of a plurality of LED elements. is there.

  The LED lighting device according to the present invention includes a plurality of LED elements connected in series, a plurality of switch elements connected in parallel to each of the LED elements, and a power source that supplies current to a series-parallel circuit of the LED elements and the switch elements. And a control circuit that controls the on / off duty of the switch element to control the luminance of the LED element by the light emission duty, and the control circuit includes a lighting pattern generation circuit that generates a timing signal for controlling the on / off duty of the switch element; The gate drive circuit is configured by a level shift circuit, a buffer circuit, and a charge pump circuit, and the control circuit has the highest potential among the plurality of switch elements. All switch elements other than the switch element connected to the The length of time to those who so regularly provided.

  Further, the vehicle headlamp according to the present invention is determined corresponding to each LED element, and an LED module in which a plurality of LED elements of the LED lighting device are arranged in a matrix and light emitted from the plurality of LED elements. And an optical unit that projects in the direction.

According to the present invention, the brightness of the LED element is adjusted by ON / OFF control of the switch element connected in parallel to each of the plurality of LED elements connected in series, and the LED element and the switch element are integrated in a series-parallel circuit. Since a power supply for supplying a constant current is provided, only one power supply is required, and the lighting device can be realized in a small size and at a low cost.
Further, the gate drive circuit of the control circuit is configured by a level shift circuit, a buffer circuit, and a charge pump circuit, and among all the switch elements, all the switch elements other than the switch element connected to the highest potential are simultaneously By periodically providing the ON period, it is possible to store the gate driving charge in the capacitor of the charge pump circuit. The use of a charge pump circuit eliminates the need to use separate isolated power supplies even when driving multiple switch elements with different reference potentials (source potentials in the case of FETs), thus reducing the size of the LED drive circuit It is possible to reduce the cost.

It is a circuit block diagram of the LED lighting device by Embodiment 1 of this invention. It is a figure which shows the structure of the control circuit in Embodiment 1 of this invention. It is a figure which shows the circuit structure of the constant current source in Embodiment 1 of this invention. It is a timing chart for demonstrating the luminance adjustment operation | movement in Embodiment 1 of this invention. It is a figure which shows the circuit structure of the constant current source in Embodiment 2 of this invention. It is a circuit block diagram of the LED lighting device by Embodiment 3 of this invention. It is a timing chart for demonstrating the relationship between the lighting state of the LED element in Embodiment 3 of this invention, and an output voltage. It is a circuit block diagram of the LED lighting device by Embodiment 4 of this invention. It is a timing chart for demonstrating the brightness adjustment operation | movement in Embodiment 5 of this invention. It is a schematic block diagram which shows the vehicle headlamp in Embodiment 6 of this invention. It is the front view and side view of an LED element module which are used for Embodiment 6 of this invention. It is a circuit block diagram of the LED lighting device by Embodiment 7 of this invention.

Embodiment 1 FIG.
Hereinafter, the LED lighting device in Embodiment 1 of this invention is demonstrated based on figures. 1 is a circuit configuration diagram of an LED lighting device according to Embodiment 1 of the present invention, FIG. 2 is a diagram illustrating a configuration of a control circuit according to Embodiment 1 of the present invention, and FIG. 3 is a constant configuration according to Embodiment 1 of the present invention. FIG. 4 is a timing chart for explaining the luminance adjustment operation in the first embodiment of the present invention.
In FIG. 1, n (n is a natural number of 2 or more) LED elements D1 to Dn are connected in series, and each LED element D1 to Dn is connected in parallel to a switching element Q1 such as an FET (Field Effect Transistor). ~ Qn are connected in parallel. That is, the drain of the switch element Q1 is connected to the anode of the LED element D1, and the source of the switch element Q1 is connected to the cathode of the LED element D1.

A control circuit 1 that controls ON / OFF of the switch elements Q1 to Qn is connected to each gate of the switch elements Q1 to Qn. Details of the control circuit 1 will be described with reference to FIG. A constant current source 2 for supplying a constant current to the LED elements D1 to Dn is connected to a series-parallel circuit of the plurality of LED elements D1 to Dn and the switch elements Q1 to Qn. The constant current source 2 is a power supply for LED element drive for supplying a constant current _{I 1} to the series circuit of the LED elements Dl to Dn. Details of the constant current source 2 will be described with reference to FIG.

  Next, the control circuit 1 used in Embodiment 1 of the present invention will be described with reference to FIG. In FIG. 2, the control circuit 1 includes a lighting pattern generation circuit 11 that generates lighting patterns for the LED elements D1 to Dn, and a gate drive circuit 12 that drives the gates of the switch elements Q1 to Qn. The lighting pattern generation circuit 11 is a circuit that generates a timing signal for controlling the on / off of the LED elements D1 to Dn and the light emission duty, and can be realized by a digital circuit using an ASIC or FPGA, a microcomputer, or the like. it can. The gate drive circuit 12 needs to supply gate drive signals of switching elements Q1 to Qn such as FETs having different source potentials, and can be realized by the level shift circuit 12a, the buffer circuit 12b, and the charge pump circuit 12c. it can. By periodically providing a period during which all switch elements Q2 to Qn other than the switch element connected to the highest potential are simultaneously turned on, charges for driving the gate are accumulated in the capacitors C1 to Cn of the charge pump circuit 12c. It is possible. In addition to the configuration shown in FIG. 2, the gate drive circuit 12 can also use a gate power source and a photocoupler that are insulated for each FET.

Next, the constant current source 2 used in Embodiment 1 of the present invention will be described with reference to FIG. In FIG. 3, the constant current source 2 can be realized by a combination of a voltage source 21 and a constant current circuit 22. The configuration of the constant current circuit 22 is configured using a switching converter such as a step-down chopper type. The constant current circuit 22 detects a current flowing through the LED elements D1 to Dn by a detection resistor Rsns connected in series with the LED elements, and inputs a detection voltage Vsence based on the detected current to the constant current control circuit 22a. The gate of the power switch element Qp connected between the voltage source 21 and the LED element D1 is controlled by a control signal from the control circuit 22a so that the current flowing through the LED elements D1 to Dn becomes constant.
The constant current circuit 22 can be connected to the anode side or the cathode side of the LED elements D1 to Dn.

Next, with reference to FIG. 4, the brightness adjustment operation of the LED elements in Embodiment 1 of the present invention will be described by taking the case where the number of LED elements D1 to Dn is n = 4 as an example.
In FIG. 4, Q1 to Q4 indicate the ON (conductive) / OFF (nonconductive) states of the switch elements Q1 to Q4 having the same names, and D1 to D4 indicate the LED elements D1 to D1 having the same names. It is a timing chart which shows the state of ON (light emission) / OFF (non-light emission) of D4. In the following description, ON and OFF are assumed to be on and off.

First, when all the switching elements Q1 switching element Q4 is turned off at the time of t0, the LED element D1~D4 is constant current driven by a predetermined current _{I 1} supplied from the constant current source 2, all the LED elements D1 to D4 emit light simultaneously. Next, when the switch element Q1 is turned on at the timing t1, both ends of the LED element D1 are short-circuited by the switch element Q1, and the LED element D1 is turned off. At this time, the current that has been flowing through the LED element D1 flows by bypassing the switch element Q1, so that the LED elements D2 to D4 remain on. Next, when the switch element Q2 is turned on at t2, the LED element D2 is turned off. Thereafter, the other LED elements are sequentially turned off in the same manner. Thus, by turning on / off the switch elements Q1 to Q4 connected in parallel to the LED elements D1 to D4, any LED element can be turned on / off at an arbitrary timing. At this time, since the current continues to flow through any of the LED elements D1 to D4 or the switch elements Q1 to Q4, the operation of the parallel circuit of the other LED elements and the switch elements connected in series is not affected.

When the above operation is repeated at a cycle TT (frequency 1 / TT), each LED element emits light with a predetermined duty. For example, the light emission duty of the LED element D1 is T1 / TT. However, T1 is the time from t0 to t1. Similarly, the light emission duty of the LED element D2 is T2 / TT, the light emission duty of the LED element D3 is T4 / TT, and the light emission duty of the LED element D4 is T3 / TT. However, T2 is the time from t0 to t2, T3 is the time from t0 to t3, and T4 is the time from t0 to t4.
Here, if the frequency 1 / TT is set to be equal to or higher than the critical fusion frequency in human vision, the blinking of the LED element is not perceived, and it appears that light is emitted at a luminance proportional to each light emission duty. The critical fusion frequency varies depending on various conditions such as luminance and light emitting area, individual differences, and the like, but is generally about 30 Hz to 60 Hz. In order not to feel flicker, it is desirable to set the frequency to 60 Hz or more.

The LED elements D1 to D4 have a characteristic that the chromaticity changes (color shift) depending on the current value. In order to suppress the change in chromaticity, the luminance is adjusted with the pulse width while keeping the current constant. It is desirable. In the present invention, brightness adjustment is performed by controlling the width of the current pulse flowing through each LED element D1 to D4 while driving all the LED elements D1 to D4 with the same constant current, so that there is little color shift. Thus, the chromaticity difference between the LED elements D1 to D4 can be reduced. Moreover, the brightness dispersion | variation between LED element D1-D4 with respect to the same brightness setting value can be made small.
Further, since the switch elements Q1 to Q4 provided in parallel with the LED elements D1 to D4 can be turned on / off at high speed, the current flowing through the LED elements D1 to D4 is an ideal rectangular wave with a fast rise / fall. Current can be passed, and the color shift can be further reduced.

Further, since the common constant current circuit 22 is used for the plurality of LED elements D1 to D4, the number of constant current circuits 22 can be reduced, and the drive circuit can be reduced in size and cost.
Further, since the LED elements D1 to D4 have a relatively low voltage and a large current, the ratio of power loss due to the internal resistance of the drive circuit may increase and the efficiency may decrease. Although the LED elements D1 to D4 are connected in series while being individually adjustable, a current corresponding to one LED element may be supplied from the constant current source 2 to the plurality of LED elements D1 to D4. The power loss due to the internal resistance of the power supply circuit can be reduced.
In addition, although FET was used as a switch element here, you may use IGBT and a bipolar transistor in addition.

  In the example shown in FIG. 4, the brightness control is performed by turning on all the LED elements (except for the LED element with completely off = zero brightness) at the beginning of one cycle and turning them off sequentially. However, the on and off timings can be set arbitrarily for each LED element. For example, it may be controlled so that all are turned off first and then sequentially turned on to finally reach the maximum number of lighting.

Embodiment 2. FIG.
Next, the LED lighting device in Embodiment 2 of this invention is demonstrated based on figures. The circuit diagram of the LED lighting device and the diagram showing the configuration of the control circuit in the second embodiment are the same as those in the first embodiment. In the second embodiment of the present invention, the constant current source has a circuit configuration different from that of the first embodiment.
FIG. 5 is a diagram showing a circuit configuration of a constant current source according to Embodiment 2 of the present invention. The constant current source 2 includes a voltage source 21 and a constant current circuit 23. As the constant current circuit 23, an active region of a transistor is formed. The linear regulator type constant current circuit used is used. As shown in FIG. 5, the constant current circuit 23 connects a transistor Tr1 and a detection resistor Rsns in series with the LED elements D1 to Dn, and inputs a detection voltage Vsence based on the current detected by the detection resistor Rsns to the base of the transistor Tr2. In this way, the current flowing through the LED elements D1 to Dn is made constant. Since this linear regulator type constant current circuit is well known, its description is omitted.
The constant current circuit 23 can be connected to the anode side of the LED elements D1 to Dn or can be connected to the cathode side.

Embodiment 3 FIG.
Next, the LED lighting device in Embodiment 3 of this invention is demonstrated based on figures.
In the present invention, the constant current source 2 is used as a power source for lighting the LED element. As described above, the constant current source 2 can be realized by combining a voltage source and a constant current circuit.
Here, when the linear regulator type constant current circuit 23 as shown in FIG. 5 is used as the constant current circuit, the power loss in the constant current circuit increases in proportion to the voltage applied to the constant current circuit 23. To do. The voltage applied to the constant current circuit is the difference between the output voltage of the voltage source 21 and the total voltage drop in the LED elements D1 to Dn. If the output voltage of the voltage source 21 is close to the voltage drop in the LED elements D1 to Dn, the power loss in the constant current circuit 23 can be reduced.

Therefore, in the invention of the third embodiment, the control circuit 1 controls the output voltage of the voltage source, and the output voltage is varied according to the number of LED elements that are simultaneously turned on. It is intended to reduce this.
FIG. 6 is a circuit configuration diagram of the LED lighting device according to the third embodiment of the present invention, and FIG. 7 shows the relationship between the lighting state of the LED elements D1 to D4 and the output voltage of the variable voltage source according to the third embodiment of the present invention. It is a timing chart.
In FIG. 6, the constant current source includes a variable voltage source 24 and a constant current circuit 23 connected to the LED elements D1 to Dn. The constant current circuit 23 is a constant current circuit as shown in FIG. The variable voltage source 24 is configured such that the output voltage Vdc is variable by the voltage control signal Vcnt from the control circuit 1. The control circuit 1 controls on / off of the switch elements Q1 to Qn connected in parallel to the LED elements D1 to Dn, and outputs a voltage control signal Vcnt corresponding to the number of lighting of the LED elements D1 to Dn. ing. The output voltage Vdc of the variable voltage source 24 is controlled by the voltage control signal Vcnt output from the control circuit 1.

Next, with reference to FIG. 7, regarding the relationship between an example of the lighting pattern of the LED element in Embodiment 3 of the present invention and the output voltage Vdc of the variable voltage source 24 at that time, the number of LED elements D1 to Dn is n. = 4 will be described as an example.
In FIG. 7, D1 to D4 indicate on (light emission) / off (non-light emission) states of the LED elements D1 to D4 having the same names, respectively, and Vdc is a variable voltage source 24 corresponding to the number of lighting of the LED elements D1 to D4. It is a timing chart which shows the output voltage.
The number of simultaneous lighting of the LED elements D1 to D4 in the period from t0 to t1 in FIG. 7 is 4, the number of simultaneous lighting of the LED elements D1 to D4 in the period from t1 to t2 is 3, and then the number of simultaneous lighting is 2 1 and 0, the number of simultaneous lighting decreases, and the number of simultaneous lighting returns to 4 again at t5.

Therefore, the control is performed so that the output voltage Vdc of the variable voltage source 24 becomes higher as the number of simultaneously lighting LED elements increases. Preferably, when the voltage that needs to be applied at a minimum for the constant current circuit 23 to operate normally is V0, the forward voltage of the LED element is Vf, and the number of simultaneous lighting of the LED elements is k, the output of the voltage source The voltage Vdc is
Vdc = k × Vf + V0
Control to be

By controlling in this way, the voltage applied to the constant current circuit 23 is always a minimum value, and when a linear regulator type constant current circuit is used, power loss in the constant current circuit 23 is reduced. Further, when the step-down chopper type constant current circuit as shown in FIG. 3 is used as the constant current circuit 23, the difference between the input voltage and the output voltage of the step-down chopper becomes small, and the ripple can be reduced.
As the variable voltage source 24, various switching converters such as a boost chopper and a forward converter can be used. Since the response speed of the switching converter is finite and a delay occurs until the output voltage Vdc reaches a predetermined value after the voltage control signal Vcnt is input, the voltage control signal is earlier than the number of simultaneous lighting changes. Vcnt may be changed.

Embodiment 4 FIG.
Next, the LED lighting device in Embodiment 4 of this invention is demonstrated based on figures.
In the fourth embodiment, an AC power source is input as a voltage source. An LED lighting device using AC power as an input can be used for lighting in a home or a store by replacing a fluorescent lamp or a light bulb.
When an AC power supply is used as an input, it is usually necessary to use a power factor correction circuit in the power supply input stage in order to reduce harmonics of the AC input current and improve the power factor. In the invention of the fourth embodiment, the power factor correction circuit will be described using the variable voltage source 24 of FIG. 6 described in the third embodiment. FIG. 8 shows a circuit configuration diagram according to the fourth embodiment of the present invention. The variable voltage source is an AC (alternating current) power source 241 and an input voltage from the AC power source 241 is converted into a pulsating direct current (DC). And a power factor improving circuit 243 for converting the output of the diode bridge circuit 242 into a DC voltage and improving the power factor. A constant current circuit 23 is connected between the series-parallel circuit of the LED elements D1 to Dn and the switch elements Q1 to Qn and the power factor correction circuit 243. Other circuit configurations are the same as those in FIG.

  In FIG. 8, the alternating current input from the AC power source 241 is converted into a sine wave pulsating current by the diode bridge circuit 242, and then converted to a DC voltage by the power factor correction circuit 243. The power factor correction circuit 243 is constituted by a step-up or step-down or step-up / step-down converter, and here, a step-up chopper type converter is used. That is, the DC voltage Vdc higher than the voltage peak of the AC power supply is obtained by on / off controlling the switching element Qr in the power factor correction circuit 243. Here, the current waveform flowing from the diode bridge circuit 242 into the boost chopper circuit varies depending on the ON / OFF timing (duty etc.) of the switch element Qr. By appropriately controlling, it is possible to control the input current waveform so that it is sinusoidal and in phase with the input voltage waveform. For example, the output voltage (pulsating current waveform) of the diode bridge circuit 242 and the input current of the power factor correction circuit 243 may be detected, and feedback control may be performed so that both have similar waveforms. In this way, if the input current waveform is controlled to have a sine wave shape and the same phase as the input voltage waveform, the power factor of the input from the AC power source 241 is improved. The output of the DC voltage obtained as the output of the power factor correction circuit 243 is applied to the series-parallel circuit of the LED elements D1 to Dn and the switches Q1 to Qn via the constant current circuit 23. Here, the output voltage Vdc of the power factor correction circuit 243 is varied in accordance with the number of LED elements D1 to Dn that are simultaneously turned on, as in the third embodiment. According to this configuration, by using the variable voltage source 24 also as a power factor correction circuit, the drive circuit can be realized in a small size and at a low cost.

Embodiment 5 FIG.
Next, an LED lighting device according to Embodiment 5 of the present invention will be described with reference to the drawings.
In the first embodiment, as shown in FIG. 4, as an example, a method of controlling brightness by turning on all LED elements D1 to Dn at the beginning of one period and sequentially turning them off is given. It was.
In this case, the voltage applied to the series circuit of the LED elements D1 to Dn becomes the maximum value, n × Vf, first in one period. When n is large, the maximum voltage applied to the series circuit of the LED elements D1 to Dn becomes very high, so that the maximum output voltage of the voltage source 21 needs to be increased.
Therefore, in the fifth embodiment, the maximum simultaneous lighting number of the LED elements D1 to Dn is limited to a predetermined value smaller than n. In FIG. 9, an example of the lighting pattern of the LED element in Embodiment 5 is shown.

As shown in FIG. 9, in this example, the maximum simultaneous lighting number is limited to 3 with respect to the serial number n = 4 of the LED elements D1 to Dn. That is, in the period from t0 to t1, the LED elements D1 to D3 are ON (on), and since the maximum number of simultaneous lighting has been reached, the LED element D4 is forcibly set to OFF (off). When the LED element D1 is turned off at t1, the LED element D4 is turned on.
By controlling as described above, the maximum output voltage of the voltage source 21 can be reduced, so that the withstand voltage of the voltage source 21 can be lowered and the peak power can be reduced. Can be realized at a lower cost.

Embodiment 6 FIG.
A vehicle headlamp according to Embodiment 6 of the present invention will be described with reference to the drawings. In the sixth embodiment, a vehicle headlamp is configured by using any one of the LED lighting devices described in the first to fifth embodiments. 10 is a schematic configuration diagram of a vehicle headlamp (headlight) according to Embodiment 6 of the present invention, and FIGS. 11A and 11B are diagrams of LED element modules used in the vehicle headlamp shown in FIG. It is a front view and a side view.
10 and 11, a plurality of LED elements Dn are arranged in a matrix on a substrate 31 to constitute an LED element module 32. The LED element module 32 is installed on the back side of the headlamp case 33, and light emitted from the plurality of LED elements Dn is determined on the front side of the headlamp case 33 corresponding to each LED element Dn. An optical unit 34 for projecting in the specified direction is provided. The LED element module 32 is connected to a drive circuit 35 that causes each of the LED elements Dn to emit light with an arbitrary luminance. Any of the LED lighting devices described in the first to fifth embodiments is used as the drive circuit 35.

  The vehicle headlamp according to the sixth embodiment uses an LED element module 32 including a plurality of LED elements Dn arranged in a matrix, and light emitted from each LED element Dn is transmitted by an optical unit 34. , Respectively, in the determined direction. Further, if the plurality of LED elements Dn are driven by the drive circuit 35, each LED element Dn can emit light with an arbitrary luminance, and the light distribution of the headlamp can be varied.

Now, functions such as AFS (Adaptive Front-Lighting System) and leveling control that improve visibility by turning the optical axis in the steering direction of the steering and irradiating light intensively in the traveling direction in the vehicle headlamps Some have Conventionally, these functions were realized by changing the light distribution by changing the direction of the headlamp unit incorporating a light source such as a lamp or LED element and an optical system such as a lens using an actuator or the like. .
By using the invention of the sixth embodiment, the light distribution can be freely changed without mechanically moving the headlamp unit. Therefore, the headlamp having functions such as AFS and leveling control can be used. It can be reduced in size and weight. Furthermore, according to the present invention, the difference in chromaticity between the LED elements can be reduced, so that projection light with little color unevenness can be obtained.

Embodiment 7 FIG.
Next, the case where the LED lighting device according to Embodiment 7 of the present invention is applied to a vehicle headlamp will be described with reference to the drawings. FIG. 12 is a diagram showing a circuit configuration of an LED lighting device according to Embodiment 7 of the present invention.
In FIG. 12, a plurality of LED elements are connected in series to form an LED element group. Each LED element group includes a high beam LED element group D _H , a low beam LED element group D _L , and a DRL (Daylight Running It is divided into three LED element groups: Lights: Daytime running) LED element group D _R. Switching element Q1~Q3 are connected in parallel in each of a plurality of LED element groups _D H which LED elements are formed by connecting in series with each _{other, D L,} D _R. Three LED element group _{D H, D L, D R} and a parallel circuit of the switch element Q1~Q3 further constitute a LED element circuitry are connected in series, a constant current source collectively to the LED element network 2 is supplying a constant current. The switch elements Q1 to Q3 are controlled to be turned on / off by the control circuit 1.

Here, if the switch elements Q1 to Q3 are on / off controlled by the control circuit 1, the LED elements of each group can emit light with arbitrary luminance. For example, during daytime, the LED element group _{D L} and the high-beam LED element group _{D H} for low beam, by turning on the switch elements Q1, Q2 connected in parallel, and unlit, DRL for LED element group D the switching element Q3 connected in parallel to _R by PWM control, it is possible to the LED element group D _R for DRL light at any brightness. Similarly, it is also possible to emit light for low beam LED element group D _L only, or only the high-beam LED element group D _H in arbitrary luminance. It is also possible to light two or three LED element groups simultaneously with arbitrary luminance.
According to the seventh embodiment, the high-beam LED element group _{D H} and the LED element group _{D L} and the DRL LED element group _{D R} for low beam, it is possible to drive only one of the power supply circuit, the power supply circuit Miniaturization and cost reduction are possible. Furthermore, since a constant and the same current is supplied to all the LED elements, the color shift is reduced and color unevenness can be prevented.

D1 to Dn: LED elements, Q1 to Qn: switch elements,
1: control circuit, 2: constant current source,
11: lighting pattern generation circuit, 12: gate drive circuit,
12a: level shift circuit, 12b: buffer circuit,
12c: charge pump circuit, 21: voltage source,
22: constant current circuit, 22a: constant current control circuit,
Rsns: detection resistor Qp: power switch element 23: constant current circuit 24: variable voltage source
31: Substrate, 32: LED element module,
33: headlight case, 34: optical unit,
35: Drive circuit, 241: AC power supply,
242: Diode bridge circuit, 243: Power factor correction circuit,
D _H : LED element group for high beam D _L : LED element group for low beam,
D _R : LED element group for DRL.

Claims (2)

A plurality of LED elements connected in series, a plurality of switch elements connected in parallel to each of the LED elements, a power source for supplying current to a series-parallel circuit of the LED elements and the switch elements, and on / off of the switch elements A control circuit that controls the brightness of the LED element by controlling the duty by the light emission duty;
The control circuit includes a lighting pattern generation circuit that generates a timing signal for controlling the on / off duty of the switch element, and a gate drive circuit that drives the gate of the switch element,
The gate drive circuit includes a level shift circuit, a buffer circuit, and a charge pump circuit,
The LED lighting device according to claim 1, wherein the control circuit periodically provides a period for simultaneously turning on all the switch elements other than the switch element connected to the highest potential among the plurality of switch elements.   The vehicle headlamp using the LED lighting device according to claim 1, wherein an LED module in which a plurality of LED elements of the LED lighting device are arranged in a matrix and light emitted from the plurality of LED elements are each The vehicle headlamp provided with the optical unit which projects in the direction defined corresponding to this LED element.

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